Butane vs Pentane: Which is Liquid & Why?

[magma_saber]

Homework Statement

There are two compounds, butane and pentane. one is a liquid at at room temp and the other is gas. which is a liquid and why?

Homework Equations

The Attempt at a Solution

I'm guessing that its pentane. For a gas to liquify, it should have a have a higher melting point, meaning that it has a higher freeing point. They both only have london dispersion forces but pentane has a greater mass so it should have a higher melting point.

 

[Borek]

More or less correct, although I am not sure if mentioning just 'greater mass' will do. Why do molecules of greater mass interact stronger?

 

[magma_saber]

im guessing as the mass of the molecules increases, so does the strength of the dispersion force acting between the molecules, so more energy is required to weaken the attraction between the molecules resulting in higher boiling points.

 

[Borek]

OK, but why higher mass means higher dispersion forces?

Hint: higher mass - more electrons, or less electrons?

 

[granpa]

im guessing as the mass of the molecules increases, so does the strength of the dispersion force acting between the molecules,.

it also means that the molecules move more slowly at any given temp

 

[magma_saber]

so since there are more electrons, higher dispersion forces?

 

[Borek]

Yes.

 

[magma_saber]

thanks for all the help.

 

[granpa]

larger molecules have the same kinetic energy as smaller molecules at a given temp but they have more surface area for intermolecular forces to act upon.